Abstract :
The infrared spectra of H2 16O and H2 18O trapped in solid argon were recorded in the range 8000–15 cm−1 at Ar/H2O molar ratios between 2000 and 20. At low concentration in water the quasifreely rotating monomer predominates, giving rise to relatively narrow rovibrational signals for the transitions involving exclusively the J=0 and 1 rotational levels, i.e. the R(0)-, Q(1)- and P(1)-type transitions. For the dimer most of the one and two quanta transitions of both proton acceptor (PA) and proton donor (PD) subunits were identified on the basis of 16O/18O isotopic substitution and of the results previously obtained in nitrogen matrix [Chem. Phys. 266 (2001) 109]. A new assignment for ν3 of PA is proposed, involving the internal rotation of PA around its symmetry axis, as observed in the gas phase and in He clusters. As in N2 matrix the 2ν1 band of PD has not been observed, which confirms the intensity weakening of the first overtone of a hydrogen-bonded OH oscillator (OHb). The same phenomenon occurs for larger polymers (H2O)n, n>2. The data analysis is focused on three points: rovibrational analysis and determination of the rotational parameters of some A1 vibrational levels; role of Fermi resonance as shaping mechanism of the νOHb band of water polymers; determination of electrooptic parameters from intensity measurements for both monomer and dimer.
